Construction of a damage risk model for footwall drifts

Current design of underground mine openings involves a great deal of uncertainty as the geotechnical domains in which mines operate are non-homogenous and highly variable in nature. Current industry practice largely follows a deterministic, Factor of Safety based approach. However, final decisions in mining operations are based on both risk and financial cost, rather than probability distributions or Factor of Safety. The overall aim of the paper is to create a damage risk model for footwall drifts in a mine using the sublevel caving production method. Both numerical and probabilistic outcomes were used to evaluate and assess risk with the aid of a risk matrix. A number of parameters including rock properties, mining-induced stresses and the location of a drift relative to the weakness zone were considered. A special emphasis was placed on the economic consequences of the assessed risk and failure potential, described in terms of drift convergence. Considered economic consequences include rehabilitation, time duration, production loss exposure and delay flexibility, with particular focus applied to shareholder value and public reputation (PR). The associated costs were then compared to find the optimum location for the drift. Keywords: risk-based design, probabilistic design, uncertainty, risk model.